Generally, a component mounting apparatus has been used widely for sequential positioning or mounting of electric components onto a substrate such as a printed circuit board. FIG. 12 shows a conventional component mounting system. The system generally indicated by reference numeral 100 includes a component supply 110 for supplying components; a transport head 120 for picking up one of the components from the component supply 110 and then turning the component upside down to orient the component in a predetermined mounting direction; a placement head 130 for receiving the component from the transport head 120 and then placing the component onto the substrate or printed circuit board in place; an imaging camera 140 for capturing an image of the component received by the placement head 130; a holder 150 for holding and then positioning the circuit board in place in the system 100; another imaging camera 160 for capturing an indication marked on the circuit board; and a controller 170 for controlling an entire operation of the system 100. The placement head 130, which is supported to move horizontally in an X-direction in FIG. 12, is equipped with a vacuum nozzle or quill capable of rotating about a vertical Z-axis.
Referring to FIGS. 13 and 14 operations of the system will be described hereinafter. In these figures, the component supply 110 is provided with a number of components 111 supported and separated from another on an expanded plate 112. The components 111 are each recognized by an imaging device or camera 113. Based upon this recognition, the controller 170 moves the component supply 110 so that one component 111a to be mounted during a subsequent mounting is positioned in a predetermined pickup position. The transport head 120 travels to a position right above the component 111a, moves downward to contact the component 111a, and then sucks the component 111a for unloading. After unloading, the transport head 120 moves upward and then travels in the X-direction to a transfer station. At the transfer station, the transport head 120 together with the component turns upside down as indicated by arrow 121. This brings the component 111a from an upside-down position into an upright position so that one surface (i.e., bottom surface with solder bumps or electrical connections) to be opposed to the circuit board is faced downwardly. The placement head 130 approaches the component 111a in the upright position from above to receive the component from the transport head 120. Then, the placement head 130 moves upward and then travels in the X-direction toward a placement station. The transport head 120, after being deprived of the component, moves back to the pickup station for a subsequent pickup operation
During the operation described above, a circuit board 151 is transported to and then held in position by the holder 150. The imaging device or camera 160 approaches the circuit board 151 to capture an indication defined on the circuit board, indicative of a reference position for mounting of the component. This captured image is then transmitted to the controller 170.
As best shown in FIG. 13, the imaging device 160 together with another imaging device 140 is mounted on an optical head 180. After recognition of the indication on the circuit board 151, the optical head 180 moves back in the X-direction toward the placement head 130 that is running in an opposite direction. Once opposed, not only the optical head 180 but also the placement head 130 comes to a halt. In this state, the component 111a held by the placement head 130 is recognized by the imaging device 140. An image captured by the imaging device 140 is transmitted to the controller 170. At this moment, a sucking nozzle of the placement head 130 for sucking and holding the component 111a is maintained in an elevated position. This prevents the nozzle from causing a conflict with the imaging device 140. Also, this sucked component 111a is held within a field of the imaging device 140.
After completion of this recognition, the placement head 130 with the component 111a restarts traveling in the X-direction again toward the mounting station. During this travel, recognition results of the component 111a and the circuit board 151 (in particular, the reference indication) are used for calculations performed in the controller 170. The controller 170 calculates displacement in the X-direction of the placement head 130 for mounting of the component 111a onto a predetermined position of the circuit board 151. Also calculated in the controller 170 are a rotational angle of the nozzle about a Z-axis and displacement of the circuit board 151. According to these calculations made by the controller 170, the placement head 130 travels in the X-direction to a position where it opposes the circuit board 151. At this moment, corrections for the nozzle and the circuit board 151 have already been completed. Then, the placement head 130 causes the nozzle to move downward, so that the component 111a is mounted in position on the circuit board 151.
After mounting, the placement head 130 releases the component 111a and then pulls up the nozzle in the Z-direction to a certain level. Then, the imaging head 180 moves in between the circuit board 151 and the placement head 130 so that the imaging device 160 determines whether the component 111a takes a predetermined position on the circuit board 151. Another imaging device 140, on the other hand, recognizes whether the placement head 130, in particular a tip end of the nozzle, carries any debris. Once this recognition has been completed, the placement head 130 moves back in the X-direction for receiving a next component. By repetition of the series of operations described above, the components on the expanded plate 112 are mounted sequentially on respective circuit boards with a cycle time of about, for example, 1.9 seconds.
However, the conventional component mounting system has several drawbacks in terms of its recognition operations. For example, for recognition of the component, the placement head 130, after it has received the component 111a, is accelerated to a certain velocity. Immediately after this acceleration, the placement head 130 comes to a temporal halt for recognition of the component 111a by the imaging device 160. This requires further acceleration and deceleration of the placement head 130 before actual mounting of the component 111a. Also, the placement head 130, after it has come to a halt, continues to vibrate for a certain period, which requires the imaging device 160 to wait until termination of the vibration in order to attain precise recognition of the component 111a. This in turn reduces an operational efficiency of the mounting.
Further, as shown in FIG. 14, in an operation for recognition of the circuit board 151, nozzle 131 of the placement head 130 is moved upward to the elevated position as indicated by arrow 135. Then, as indicated by arrow 145, the optical head 180 moves in between this elevated nozzle 131 and the circuit board 151 for imaging by the imaging devices 140 and 160. A distance between the elevated nozzle and the circuit board, indicated by letter H, is designed to be about 40 mm, for example, in order to prevent interference of the optical head 180 with the nozzle 131, and also to ensure a proper imaging operation of the optical head 180. Elevation of the nozzle 131 requires 0.1 seconds even by use of a high-speed voice coil motor.
Furthermore, the conventional mounting system is equipped with an interlock to avoid interference of the optical head 180 with the placement head 130 during recognition operations by the optical head 180 before and after mounting. This complicates structure of the mounting system 100 and makes the system less economical.
Moreover, a conventional recognition procedure requires the placement head 130 and the optical head 180 to travel along complicated passes, respectively. This in turn requires the mounting system to have a greater number of drive shafts and acceleration/deceleration operations, which further reduces positional precision of a moving part and thereby imaging quality.